1. Field of the Invention
The present invention relates to a method of etching an insulating film and a method of forming an interconnection layer, more particularly relates to a method of etching an insulating film including an organic-based dielectric film of a low dielectric constant and a method of forming an interconnection layer which forms openings in the insulating film by etching and buries a conductor there to form the interconnection layer.
2. Description of the Related Art
Recent semiconductor integrated circuits are reaching the next generations of miniaturization and integration in just three years. Integration of more than several million elements on a several mm square semiconductor chip is becoming necessary.
To achieve such miniaturized and integrated semiconductor devices, the design rule has been reduced to 70% of that of the previous generation. For example, the gate length of the gate electrodes of transistors and the area occupied by capacitors in a DRAM etc. have been reduced. Along with this reduction, the semiconductor devices have also been increased in speed.
Along with the increasing miniaturization and integration of semiconductor devices, it is no longer enough to just miniaturize planar elements in a single interconnection layer of the semiconductor device. Technology for multilayer interconnections stacking two or more interconnection layers has become essential.
On the other hand, there is a growing demand for greater functions and faster operating speeds of the elements in the above highly integrated semiconductor devices. For example, in the above miniaturized multilayer interconnection layer, the signal delay due to the increase of the capacity between interconnection layers has become a factor obstructing the increase of the speed of device operation. This is becoming a serious problem.
To solve the problem, the method of forming an interlayer insulating film by an insulating material having a lower dielectric constant than the conventionally used silicon oxide (dielectric constant of 4.3) so as to reduce the capacity between the interconnection layers has been studied.
Insulating materials having a lower dielectric constant than silicon oxide may be roughly divided into organic-based materials and inorganic-based materials.
The leading inorganic-based material, SiOF, has come under attention as a soon to be realized technique since it can be easily formed by, for example, plasma chemical vapor deposition (CVD) method.
On the other hand, as organic-based materials, there are many materials having a low dielectric constant of 2 to 3.0 such as polyarylethers. There are great hopes for their commercial use in the next generation on.
The method of producing a semiconductor device reduced in capacity between interconnection layers by partial use of an organic-based material of a low dielectric constant for the interlayer insulating film as described above is for example as follows.
First, as shown in FIG. 1A, a not shown semiconductor element such as a transistor is formed on a silicon semiconductor substrate 10, then for example aluminum is deposited above the semiconductor substrate 10 or above the not shown insulating film and patterned to form a first interconnection layer 11.
Next, for example, a liquid polyarylether is dropped on the substrate, spread uniformly by spinning the substrate, and then baked and cured to form a first interlayer insulating film 12 composed of the polyarylether. Then, a second interlayer insulating film 13 composed of silicon oxide is formed on the first interlayer insulating film 12.
In this way, the interlayer insulating film 14, that is, a stacked insulating layer comprised of the first interlayer insulating film 12 and the second interlayer insulating film 13, is formed.
Next, a resist film R having a pattern of openings of contact holes is formed by photolithography on the interlayer insulating film 14.
Next, for example, as shown in FIG. 1B, etching is performed by a magnetron enhanced reactive etching system using C4F8/CO/Ar/O2 as an etching gas to form contact holes CH penetrating through the second interlayer insulating film 13 and expose the first interlayer insulating film.
Then, for example, as shown in FIG. 2A, etching is performed using an electron cyclotron resonance (ECR) type plasma etching apparatus and using oxygen (O2), which is usually used in etching an insulating film comprised of an organic-based material, so as to form contact holes CH penetrating through the interlayer insulating film 14 comprised by the first interlayer insulating film 12 and the second interlayer insulating film 13 and expose the upper surface of the first interconnection layer 11.
In the above etching, the resist film R comprised by the organic-based material is removed by etching.
Further, the outer layer portion of the inner wall surface of the contact holes CH of the first interlayer insulating film 12 is oxidized by etching using oxygen and a damage layer 12′ is formed.
Next, as shown in FIG. 2B, a titanium nitride film or a stacked film of titanium nitride and titanium etc. is formed by long distance sputtering of other sputtering to form a bonding layer 15.
Next, for example, the contact holes CH is buried with tungsten or another conductor by a CVD method to form plugs connecting to the first interconnection layer 11, then a second interconnection layer is formed over this so as to connect with the plugs. Next, other semiconductor elements can be formed.
By the above procedures, a semiconductor device with a first interconnection layer and a second interconnection layer respectively formed above and below an interlayer insulating film connected by plugs buried in contact holes penetrating through the interlayer insulating film may be formed.
Summarizing the problems to be solved by the present invention, in the above method of production of a semiconductor device, since a damage layer 12′ is formed on the outer surface of the inner wall surface of the contact holes CH of the first interlayer insulating film 12 due to oxidization by the etching using oxygen (O2) in the process of etching the first interlayer insulating film 12 to form the contact holes CH, a gas G ends up being released from the damage layer 12′ as shown in FIG. 3 in the process of burying the contact holes CH with tungsten or another conductor by CVD etc. As a result, the contact holes cannot be buried with the tungsten well and voids V are formed. These cause the problem of poor conduction.
To avoid this problem, there is the method of using a nitrogen gas (N2), which has a lower reactivity than oxygen (O2), for etching an insulating film made from an organic-based material. In this case, however, another problem arises that the etching speed becomes remarkably lower compared with the case of using oxygen gas and the throughput in the process of production of the semiconductor device falls.